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Spine
Lumbar vertebra, 5 in total, lies between the thoracic and the sacrum. The bodies increase in breadth from above down, with progressive widening of the articular processes. * The vertebral body appear kidney shaped (transverse >AP) * Transverse processes extend out laterally, long and flat on L1-4, small at L5 * Pedicle are stout and project directly posteriorly forming the upper and lower margins of the intervertebral foramina * The lamina are strong and do not show a downward slope as in the thoracic vertebrae * The articular processes are characteristic. Superior and inferior articular processes with pars interarticularis between. The facet joint is oblique (not coronal). The superior faces upwards, medially and backwards and concave. * Intervertebral foramen ** Aperture giving exit to segmental spinal nerves and entrance to vessels ** Oriented laterally below pedicle ** Boundaries *** Superior & inferior pedicles of adjacent vertebrae *** Ventral boundary is dorsal aspect vertebral body above and intervertebral disc below *** Dorsal boundary is joint capsule of facets and ligamentum flavum ** Vertical elliptical shape in lumbar region *** Vertical diameter 12-19 mm *** Transverse diameter from disc to ligamentum flavum ~ 7 mm; thus, little room for pathologic narrowing Joints * Intervertebral disc ** Outer annulus fibrosus (alternating layers of collagen fibers) ** Inner annulus fibrosus (fibrocartilaginous component) ** Transitional region ** Central nucleus pulposus (elastic mucoprotein gel with high water content) * Facet (zygapophyseal) joints ** Facet joints oriented obliquely ** Superior facet: Concave, faces dorsomedially to meet inferior facet from above ** Inferior facet: Faces ventrolaterally to meet superior facet from body below Ligaments * Anterior and posterior longitudinal ligaments, interspinous and supraspinous ligaments * Ligamentum flavum ** Thick in lumbar region ** Connects adjacent lamina ** Extends from capsule of facet joint to junction of lamina with spinous process, discontinuous in midline Muscles * Erector spinae: Poorly differentiated muscle mass composed of iliocostalis, longissimus, spinalis * Multifidi (best developed in lumbar spine) * Deep muscles: Interspinalis, intertransversarius * Quadratus lumborum & psoas muscles Variants: Transitional lumbosacral bodies (up to 25% in normal). Sacralization and lumbarization may be similar in appearance, requiring evaluation of entire spinal axis to define anatomy and correct level nomenclature * Sacralization of lumbar body: Spectrum extending from expanded transverse processes of L5 articulating with top of sacrum to incorporation of L5 into sacrum * Lumbarization of sacrum: Elevation of S1 above sacral fusion mass assuming lumbar body shape * Lumbar rib * Transverse process of fourth lumbar arise from vertebral body * Foramen behind transverse process formed by mamillary and accessory processes united by bony bridge. * pseudoarthrosis of L5/S1 * pars interarticularis spurs The fifth lumbar vertebra (L5) is the largest of the five lumbar vertebrae and is considered an atypical vertebra due to its shape. L5 is the largest, most inferior lumbar discovertebral unit in the vertebral column.a Articulations of the zygapophyseal (facet) joints permit flexion/extension and abduction movements. Rotation is greatly limited, and may occur only slightly at the lumbosacral joints. Unlike other lumbar vertebrae, L5 has a distinct transverse process described below. Anterior components of L5 include: * body: large, transverse width > AP diameter ** axial view: oval/kidney-shaped ** sagittal view: wedge shaped, taller anteriorly, shorter posteriorly Posterior components of L5 include: * pedicles: project directly posteriorly * transverse processes (features below unique to L5): ** short, massive, pyramidal ** base is more anterior and attached from pedicle to the lateral side of vertebral body * lamina: broad, thick, overlap minimally * articular process: superior and inferior (with pars interarticularis between) * facet joints: obliquely oriented, cylindrically shaped articular surfaces ** superior articular facets are concave and face posteromedially ** inferior articular facets are convex, and face anteriorly * spinous process: thicker and shorter, roughly horizontal Articulations * superior articular facet with inferior articular facet of L4 * inferior articular facet with superior articular facet of sacrum: the L5 inferior articular facets face well forward and are received by backward-facing facets of the sacrum * intervertebral discs: superior and inferior Relations * anteriorly: anterior longitudinal ligament * posteriorly ** posterior longitudinal ligament ** ligamentum flavum ** interspinous ligament ** supraspinous ligament ** erector spinae muscle ** external vertebral venous plexus (lying within muscle) * laterally ** Iliolumbar ligament ** lumbar fascia ** quadratus lumborum muscle ** intertransverse ligaments ** regional/segmental lumbar arteries and veins * superiorly: L4/5 intervertebral disc * inferiorly: L5/S1 intervertebral disc * centrally ** vertebral foramen ** cauda equina ** basivertebral veins and internal vertebral venous plexus Variant anatomy * lumbosacral transitional vertebrae. Ossification of Lumbar (L1-5) * Three 1° ossification centers per vertebra ** Centrum (1), posterior vertebral neural arch (2) * Seven 2° ossification centers per vertebra, ** Spinous process apex (1), transverse process apex (2), annular epiphysis (2), base of mamillary processes (2)